I'm writing in Arduino for an STM32F103 processor on a 'blue pill' dev board. Megunolink is working fine except for the 'Arduino Upload Monitor'. The COM Port is always locked out. I realize this may be due to a different tool-chain, maybe not using AVRDude? Not a big problem, but if there's a simple fix that would be great. Thanks for any info.

Hi, you are exactly right. We rely on putting wrappers around the programmers (avrdude and esptool). What software is used for programming STM chips from the arduino IDE? We might be able to add a wrapper for that tool as well.

Sorry for not responding sooner. The STM32 uses the GNU tool chain, specifically arm-none-eabi-g++. Part of the Arduino setup is to install the Arduino SAM boards from the boards manager, which I think installs ARM support.